All good advise : it is clearer what I should do next.
Is £50 decent price for a Seagate 1TB "CE" drive?
Current firmware can format a 2TB drive so if that's not much more dosh ...
I paid about £80 for a 2TB Seagate Pipeline (ST2000VM003) a while back. Amazon have them now for £73 and they are not usually the cheapest. The 2TB drives are cheaper per GB than the 1TB ones.
If you are going to replace the drive and want your recordings copied over, the easiest way is to install the new drive and copy from the old drive in a USB caddy, connected to one of the USB ports. Install the auto-unprotect package on the old drive first before replacing it. It will scan the drive and unprotect (but not decrypt) any high def. recordings.
When you have installed the new drive and formatted it you will have to reinstall the custom firmware packages again: you will get the installation web page when you open Web-If.
If you then connect the old drive to a USB port, it will mount three partitions. The second one is where the recordings are. If you copy them back to the new drive, using the remote control, the recordings will be decrypted in the process too.